FITS metadata for lsst.afw.image Exposures

ExposureInfo and contents such as Filter and VisitInfo can be stored as FITS header keywords. The catalog schemas are described in ExposureInfo.cc, Filter.cc, and VisitInfo.cc. This page describes the equivalent FITS header keywords.

HDU 0

Keyword	Format	Units	Accessor [1] and description
DETNAME	str		Detector.getAmpInfo Detector name.
DETSER	str		Detector.getAmpInfo Detector serial number.
EXPID	long int		ExposureInfo.getId Exposure ID.
EXPTIME	float	sec	VisitInfo.getExposureTime Exposure duration (shutter open time).
DARKTIME	float	sec	VisitInfo.getDarkTime Time from CCD flush to readout, including shutter open time (despite the name)
DATE-AVG	ISO8601		VisitInfo.getDate Date at middle of exposure, at boresight. No time zone character allowed.
TIMESYS	str		Must exist and must be set to "TAI" if DATE-AVG is present.
TIME-MID	ISO8601		VisitInfo.getDate Deprecated; read if DATE-AVG not found, for backwards compatibility. Date at middle of exposure. The time zone character must exist and must be "Z". Note: TIME-MID is always UTC (even if the comment claims it is TAI) and TIMESYS is ignored.
MJD-AVG-UT1	float	MJD	VisitInfo.getUt1 UT1 date middle of exposure, at boresight
AVG-ERA	float	deg	VisitInfo.getEra Earth rotation angle at middle of exposure, at boresight.
BORE-RA	float	deg	VisitInfo.getBoreRaDec Position of boresight, ICRS RA.
BORE-DEC	float	deg	VisitInfo.getBoreRaDec Position of boresight, ICRS Dec.
BORE-AZ	float	deg	VisitInfo.getBoreAzAlt Position of boresight, refracted apparent topocentric Az.
BORE-ALT	float	deg	VisitInfo.getBoreAzAlt Position of boresight, refracted apparent topocentric Alt.
BORE-ROTANG	float	deg	VisitInfo.getBoreRotAngle Orientation of rotator at boresight.
ROTTYPE	str		VisitInfo.getRotType Type of rotation; one of: UNKNOWN SKY: position angle of focal plane +Y measured from N through E. HORIZON: position angle of focal plane +Y measured from +Alt through +Az. MOUNT: the position sent to the instrument rotator; the details depend on the rotator.
OBS-LONG	float	deg	VisitInfo.getObservatory Longitude of telescope.
OBS-LAT	float	deg	VisitInfo.getObservatory Latitude of telescope (positive eastward).
OBS-ELEV	float	m	VisitInfo.getObservatory Geodetic elevation of telescope (meters above reference spheroid).
AIRTEMP	float	C	VisitInfo.getWeather Air temperature.
AIRPRESS	float	Pascals	VisitInfo.getWeather Air pressure.
HUMIDITY	float	%	VisitInfo.getWeather Relative humidity.
AR_HDU	int		HDU containing the archive used to store ancillary objects
COADD_INPUTS_ID	int		Archive ID for coadd inputs catalogs
AP_CORR_MAP_ID	int		Archive ID for aperture correction map
PSF_ID	int		Archive ID for the Exposure’s main Psf
WCS_ID	int		Archive ID for the Exposure’s main Wcs
VALID_POLYGON_ID	int		Archive ID for the Exposure’s valid polygon
ARCHIVE_ID_[name]	int		getComponent("[name]") Archive ID for an arbitrary Exposure component

HDUs 1 to 3

Keyword	Format	Units	Accessor [1] and description
CRPIX1A	double	pixels	X axis reference pixel, always 1.0.
CRPIX2A	double	pixels	Y axis reference pixel, always 1.0.
CRVAL1A	double		Exposure.getXY0 Access as exposure.getXY0[0].
CRVAL2A	double		Exposure.getXY0 Access as exposure.getXY0[1].
CTYPE1A	str		Always "LINEAR".
CTYPE2A	str		Always "LINEAR".
CUNIT1A	str		Always "PIXEL".
CUNIT2A	str		Always "PIXEL".

[1]	(1, 2) Unless otherwise noted, each object is contained in the ExposureInfo and has a getter. Thus to get VisitInfo use exposure.getExposureInfo().getVisitInfo(). In some cases a direct shortcut is also available, e.g. exposure.getFilter() is a shortcut for exposure.info.getFilter().